Carb adjustment question

[GratefulPhish]

Bear with me here, I am learning...

When cold, this is how my idle cam and idle cam adjustment screw sit. Should I back that screw out until it barely touches the lowest step?

Thanks

[68IHscout]

No touchy a little gap on the bottom.

[ashman40]

While I have called that adjustment screw at the end of the throttle arm a "fast idle screw" in the past, that is probably incorrect. While it does control the opening of the throttle as it rests on the different steps of the fast idle cam, its adjustment is done to control the opening of the throttle plate when it is NOT resting on the cam steps.

Only adjust that screw when it is resting on the lowest level of the cam. Notice I didn't use the word "step" to avoid any misunderstanding. You want to adjust it so the throttle plate is fully closed when the choke is OFF while making sure the edges of the throttle plate/butterfly are NOT resting on the inside of the carb throat. This is done by loosening the screw until it is just about to touch the lowest level of the cam and then screw it in 1/4-turn. Now the throttle arm screw is resting on the cam and the throttle plate is not resting on the inside of the throat... all while the throttle plate is fully closed so no air flows around the edges. At warm idle, all air flow thru the carb is thru the hole in the throttle plate or thru the bypass circuit which is controlled by the large bypass screw on the left side of the carb. This allows you to control the idle rpms with the bypass screw.

Incorrectly setting this throttle plate adjustment screw results in scoring of the inside of the of the throat by the throttle plate... or prematurely exposing the progression circuit holes in the side of the throat while the car is idling.

The carb choke adjustment is done ONLY using the choke coil on the right side of the carb. Rotating the choke coil one way or the other controls the amount of time the choke remains ON. Unlike on some other carbs, there is no adjustment to control how much the choke holds the butterfly open.
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AshMan40
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[glutamodo]

Fast Idle Cam Screw is an OK term, because it does bear on the fast idle cam.

I usually say Throttle Arm Stop Screw myself though.

Technically, there is a way to alter the warm-up time of the choke unrelated to the rotational adjustment, and that is to put in a choke element with a different wattage heating coil inside it. (or guess if you want a delay, you could wire in a resistor in-line with the power feed to the choke element) However I think only original parts made by DVG for VW had any indication of this on them... 78 and 60. In the aftermarket I think they are all about the same, but not sure if they are the J or L version.

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[beetlenut]

Just to clarify, you need to make two adjustments to set your carb up from the way it sits now. When your engine is cold, the end of the Fast Idle Cam Screw should be touching the top most step of the fast idle cam. You'll notice by the slot in the cam's left side, that it can rotate some more clockwise. So you adjust the choke (on the opposite side of the carb) to make that happen.

Then after you start the car and let it completely warm up, the fast idle cam will have rotated counter clockwise to its lowest step. That's when you make the second adjustment for the fast idle cam screw.
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[Tim Donahoe]

When the engine is cold, when you pull back on the throttle arm, does the stepped cam move counterclockwise, so that the screw is then on the lowest (non-stepped) portion of the cam?

On a cold engine, it’s normal for your set screw rest on the lower step, or even higher. While on a step, the screw will be in direct contact with the stepped cam—no space. However, when you pressing on the accelerator cable, your choke—I’d adjusted properly—will turn and allow your stepped cam to also turn, so that the screw is on the unstopped bottom of the cam. This position is where you might worry about spacing.

As long as set screw is on a step, there will always be contact.

Tim
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